Recently, Optical Coherence Tomography (OCT) which forms images indicating a surface form and an internal form of an object to he measured by using light beams from a laser light source and so forth attracts attention. Since the OCT does not have such invasiveness to the human body that an X-ray CT has, development of application thereof, in particular, in the medical field and the biological field is expected. For example, in the field of ophthalmology, a device for forming images of the eyeground, the cornea and so forth enters into the stage of practical application. In the OCT, a signal is obtained by bifurcating light from a light source into signal light with which a measurement object is to be irradiated and reference light which is reflected by a reference light mirror without irradiating the measurement object with it, multiplexing the signal light which is light reflected from the measurement object and the reference light, and making them mutually interfere.
The OCT is roughly divided into a Time-domain OCT and a Fourier-domain OCT depending on a method of scanning a measurement position in its optical axis direction (hereinafter, referred to as a z-scan). FIG. 1 is a schematic diagram of an optical system of the Time-domain OCT. In this system, the z scan of a measurement object 104 is performed by using a low coherence light source as a light source 101 and scanning a reference light mirror 102 as shown by an arrow 103 at measurement. Thereby, only a component which is included in signal light 105 and matches reference light 106 in optical path length interferes with it and a detection signal as shown in FIG. 2 is obtained from a detector 107. A desired signal as shown in FIG. 3 is demodulated by performing envelope detection on the signal shown in FIG. 2.
On the other hand, the Fourier-domain OCT is further divided into a Swept-source OCT and a spectral-domain OCT. In the Swept-source OCT, the z can is performed by using a wavelength sweeping type light source which can sweep the wavelength of light to be emitted as the light source and sweeping the wavelength of the light source at measurement, and the desired signal is obtained by Fourier-converting wavelength dependency (an interference spectrum) of the intensity of detected interference light. In the spectral-domain OCT, to diffract generated interference light by a spectroscope and to detect the intensity of the interference light (the interference spectrum) of each wavelength component by using a wide bandwidth light source as the light source corresponds to performing the z scan. The desired signal is demodulated by Fourier-converting the obtained interference spectrum.
In the conventional OCT devices as mentioned above, a spatial resolving power in a depth direction is determined by a spectral width of the light source, and heightening of the resolving power has been promoted by widening the spectral width.
In addition, there is a need for speeding-up aiming at biometry, and measurement in a z-axis direction is sped up by realizing mirror drive-less in the abovementioned Fourier-domain OCT (Patent Literature 1). In addition, in speeding-up in x y axis directions, there is a plane bulk acquiring technology using a surface light source which is called a “full-fielding” technology, and a Polarization Sensitive OCT device which utilizes the full-fielding technology is also proposed (Patent Literature 2).
In addition, as an optical tomographic observation device which is already used in the field of bio-imaging, a confocal laser microscope is known. The confocal laser microscope is a kind of the microscope which can reconstruct an image of high resolution and three-dimensional information, and has a characteristic that a distortion-free image can be obtained even from a thick sample having such a complicated structure that a plurality of reflection surfaces are present. A plurality of pieces of data on observation images which have been picked up at every minute point are reconfigured by a computer and thereby a three-dimensional whole image is acquired.
As the theoretical and greatest characteristic of the confocal microscope, a confocal optical system can be given. In the confocal optical system, a point light source is projected onto a sample and, further, a pin hole and a detector (mostly, a photomultiplier tube) are arranged at a re-imaging position of the sample which is called a detection surface. Here, since all of the point light source, the sample, and the pin hole (an imaging surface position) are at conjugated positions, it is called the confocal optical system. By taking such a configuration, when a sample observation image which is at a certain lens position, that is, in a certain focal length state is to be acquired, since light reflected from different depths of focus is cut (light-shielded) by the pin hole arranged on the confocal optical system, the distortion-free image can be acquired. On the other hand, since in a general optical microscope, also the light reflected from the different depths of focus is incident upon the detector together therewith, a distorted image is made. Optical tomographic observation becomes possible by acquiring the image at each focal length by using the confocal optical system and reconstructing a result of observation at the plurality of focal lengths on a computer (Non-Patent Literature 1).